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<p class="header"><a class="header" href="intro.htm">Orbiter</a> &gt; <a class="header" href="mfd.htm">MFD</a> &gt; HSI</p>

<h1>Horizonal Situation Indicator MFD</h1>

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<td width=50% align=center><a href="mfd_hsi_ctrl.htm">Controls</a></td>
<td width=50% align=center><a href="mfd_hsi_disp.htm">Display components</a></td>
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<p>The Horizontal Situation Indicator (HSI) consists of two independent displays. Each display can be slaved to a NAV receiver and show directional and relative bearing information. The instruments accept data from surface-based transmitters such as VOR and ILS. The function is similar to instrument navigation systems found in aircraft.</p>

<p>The display consists of a gyro-compass indicating the current heading at the 12 o'clock position. The yellow arrow in the centre of the instrument is the course arrow or Omni Bearing Selector (OBS). When the slaved NAV radio is tuned to a VOR transmitter, the OBS can be adjusted with the OB- ( <kbd class="ctrl">Shift</kbd> <kbd>[</kbd> ) and OB+ ( <kbd class="ctrl">Shift</kbd> <kbd>]</kbd> ) keys. For ILS transmitters, the OBS is automatically fixed to the approach direction.
The middle section of the course arrow is the Course Deviation Indicator (CDI). It can deflect to the left and right, to show the deviation of the OBS setting from the current bearing to the NAV sender. If the CDI is deflected to the left, then the selected radial is to the left of the current position.
In the lower left corner of the instrument is the TO/FROM indicator. "TO" means that you are working with a bearing from you to the ground station; "FROM" indicates a radial from the ground station to you.</p>

<p>When tuned to an ILS (localiser) transmitter, the instrument shows an additional horizontal glideslope bar for vertical guidance to the runway. If the bar is centered in the instrument, you are on the correct glide slope. If it is in the upper half, the glide slope is above you, i.e. you are too low. If it is in the lower half, the glide slope is below you and you are approaching too high.</p>

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